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大黄素作为天然蒽醌类染料,因其在可见光照射之下的良好光致生物活性而越来越受关注。考虑到含时密度泛函理论(TD-DFT)在研究光敏剂光物理化学过程中应用成功,本文用其研究大黄素激发态的各种性质,并用连续介质模型(PCM)讨论溶剂效应对激发态行为的影响。发现:(1)在无氧条件下,溶剂中大黄素可损伤DNA,原因是碱基对与大黄素阳离子之间的电子转移所致,并非由其三重激发态与碱基对直接作用而引起。而阳离子的产生是依赖容剂中2个邻近的三重态大黄素分子间的自离子化反应;(2)在有氧的环境中,大黄素的去激发能可以提供足够的能量与氧气之间发生能量转移而产生单重态氧;溶剂效应降低大黄素的电离势及电子亲和势,使其在水中更容易放出电子。当大黄素被还原后,在气相中氧的氧化能力不足以夺取大黄素负离子的电子而产生超氧阴离子,而在溶剂中这一反应却可能发生。
Emodin, as a natural anthraquinone dye, has drawn increasing attention due to its good photobiological activity under visible light irradiation. Considering the successful application of time-dependent density functional theory (TD-DFT) in the research of photosensitizer photophysics, this paper studies various properties of emodin excited states and discusses the effect of solvent effect on excitation The impact of state behavior. It was found that: (1) emodin can damage DNA in solvent under anaerobic conditions because of the electron transfer between base pairs and emodin cations, not caused by the direct interaction between triplet excited states and base pairs . While the generation of cations depends on the self-ionization reaction between two adjacent triplet emodin molecules in the bulk. (2) The de-excitation energy of emodin in aerobic environment can provide enough energy between oxygen The transfer of energy produces singlet oxygen; the solvent effect reduces the ionization potential and electron affinity of emodin, making it easier to emit electrons in water. When emodin is reduced, the oxygen oxidation capacity in the gas phase is insufficient to capture the electrons of the emodin anion to produce superoxide anion, which may occur in a solvent.